1. Field of the Invention
The present invention relates to a wireless positioning server using clock offset compensation and a wireless positioning method using the same, and more particularly, to a wireless positioning server using clock offset compensation that may estimate a precise position of a tag requiring position information by effectively predicting information regarding a distance between a beacon for performing positioning and the tag requiring position information, and a wireless positioning method using the wireless positioning server.
2. Description of the Related Art
An indoor/outdoor wireless positioning technique is essential to implementation of a location based service (LBS) technique that has recently emerged. Since signals can be received from a global positioning system (GPS) that are clock-synchronized between satellites outdoors, positioning can be performed using a GPS technique. However, indoors where signals cannot be received from the GPS, a wireless positioning system that is suitable for an indoor environment, is required. Thus, research into a wireless positioning technique that is suitable for indoor wireless positioning, has proceeded briskly.
In general, information regarding a distance between a beacon of a positioning system and a tag that requires position information is required to perform wireless positioning. A wireless positioning technique that is based on time information, such as time of arrival (ToA) or time difference of arrival (TDoA), is mainly used to estimate the information regarding the distance between two devices, i.e., between the beacon and the tag.
Time information between the beacon and the tag for wireless positioning is estimated based on clock information between beacons. However, since an independent clock offset exists in clocks of the beacons, an error occurs in the estimated time information. Due to the effect of the clock offset, an error occurs in the result of estimating the distance between the beacon and the tag.
Although a relative clock offset in the beacons is a minor difference in units of part per million (ppm), the error in the clock information causes an error in the time information. Thus, the wireless positioning system that is based on time information, is very sensitive to the clock offset. Thus, clock offset compensation between the beacons is essential to a low error in position information that requires indoor wireless positioning.
In order to solve these problems, in the related art, Korean Patent Application Publication No. 2011-0051319 discloses a method of reducing a position estimating/updating period of a movement node and improving precision of positioning through line compensation of an error element in a wireless positioning network. However, in the related art, a two way ranging (TWR) method is used to estimate a position of a tag. Thus, the tag should transmit pulse twice, power consumption of the tag is large. In addition, since the ToA technique is used, a process in which the tag participates in time synchronization, is additionally required.